Igniter plug



United States Patent O IGNrrER PLUG Application December 23, 1957,Serial No. 704,466

6 Claims. (Cl. 313-130) This invention relates to igniter plugs and hasas one of its objectsan improved igniter plug which is adapted toproject an especially large holt spark. Another object is to provide anigniter plug particularly suitedl for vuse in rocket and gas turbineengines wherein an especially large hot spark is desirable or essentialto assure Vinitiation of combustion.

, Brieily theV invention comprehends an igniter plug wherein the sparkgap is recessed from vthe tiring end of the igniter and is formed by `anannular ground electrode which is spaced, along the axis of the igniter,from the center electrode by a ring-shaped insulator having an innerdiameter larger than that of the ground electrode. The annular groundelectrode with its relatively small bore, as compared to that of theinsulator, serves to restrict passage of the electrical discharge andfunnel it to form a pencil of ame which projects a considerable distancefrom the end of the igniter. In the preferred embodiment one or both ofthe electrodes are made ofcarbon, portions of which vaporize or spatterduring the electrical discharge to'thereby further assist sparkpropagation. ,f

Other features,V objectsfand advantages of the invention will appearVmore clearly from the following detailed description thereof made withreference to the appended drawings in which:

Figure 1 is a side view in partial section of an igniter constructed inaccordance with the invention; and

Figure 2 is an enlarged view in section ofthe firing end of the ignitershown in Figure 1.V

Referring now to the drawings, Z is a tubular metal shell internallythreaded at the lower or iiring end thereof as shown at 4, and having amounting ange 5 for securement of the iginiter in the combustion chamberof a gas turbine engine, rocket engine or the like. Secured within theshell is an elongated ceramic insulator 6, the lower end of whichterminates short of the lower end of the shell. The insulator has acylindrical through-bore which is of enlarged diameter at the firing endof the plug thereby forming a cylindrical recess as shown at 8. Raisedportion 9 on the internal surface of the shell is for the purpose ofmore snugly receiving and therefore centering insulator 6 within thetubular shell.

A metal centerwire 10 is secured within the insulator bore andterminates with a head portion 12 located within the cylindrical recess8. The upper end 11 of the centerwire forms one of the electricalcontact terminals for the igniter, the other contact being formed by themetal shell 2 from which the centerwire is separated by the insulator 6as shown. A carbon button 14 which forms the center electrode of theigniter plug is positioned within the recess 8 against and in electricalcontact with the head portion 12 of the centerwire. This button has acylindrical projection 16 of reduced diameter which extends snuglywithin a ring 18 made of ceramic insulating material such as alumina,magnesia, glass or the like. The ground electrode of the igniter isformed by a carbon ring 20 which is partially within recess 8 andpositioned con- Patented Feb. 17, 1959 ,ICC r 2 centrically against theinsulator ring 18. The length of insulator ring 18 is greater than thatof projection 16 on the center electrode, the exposed inner surface 21of the insulator ring forming a cylindrical-shaped spark gap between thetwo carbon electrodes. The assembly of the two electrodes and theinsulator ring is held securely within the recess 8 by means of a metalring 22 which has a tapered centerbore converging toward the groundelectrode and which is threadedly engaged with the lower end 4 of theshell to thereby bear against the ground electrode. This metal ring 22also serves to electrically connect the ground electrode to the sparkplug shell. 'Four equally spaced slots, three of which are shown at 24,26 and 28 in Figure 2, provide a suitable tool engagement means tothread the ring 22 into the end Y of the shell.

In accordance with the invention, the bore of carbon ring 20 is smallerthan that of insulator ring 18 such that the ring 2l) serves as a slightrestriction to the passage of electrical discharges outwardly from theend of the igniter plug. For optimum spark propagation, the borediameter of ring 20 should be from 33% to 75% of the bore diamelter ofinsulator ring 18; that is, the bore diameter of ring 20 should be nolarger than three-fourths, and no smaller than one-third, of the borediameter of ring 18. In the particular embodiment which is shown in thedrawings, but not to exact scale, the bore diameter of ring 20 is .06inch or about 60% of the bore diameter of insulator ring 18 which is.098 inch. The optimum length for the spark gap 21 will, of course, bedetermined by the amount of electrical energy to be applied. Theparticular embodiment shown operates on volts, 25 amps, and the lengthof gap 20 is.025 inch.

While car-bon is preferred for the electrodes, other referenceto aparticular embodiment thereof, it is not to'.

be so limited since changes and alterations therein may be made whichare within the full and intended scope of the claims which follow. Forexample, if desired the spacer ring 18, instead of being made solely ofan insulating material, may be made of, or its internal surface providedwith a coating of, a semi-conductive material to form a so-calledcreep-gap or'low tension type spark gap, and the claims are intended tocomprehend such a substitution, it being understood that the ring needonly be an insulator in the sense that it must electrically separate theelectrodes to form a spark gap.

What is claimed is:

1. An igniter comprising a tubular metal shell, an insulator securedwithin said shell and having a centerbore enlarged at one end thereof toform a recess, a metal centerwire within said centerbore terminatingwith a head portion positioned within said recess, an insulator memberhaving an opening therethrough and positioned in said recess, a centerelectrode positioned between said centerwire head portion and one sideof said insulator member, said center electrode having a projectionextending partially through the opening in said insulator member, and aground electrode having an opening therethrough aligned with the openingin said insulator member and positioned against the otherside of saidinsulator member so as to be in spaced relationship to said projectionto form a spark gap therewith, the opening in said ground electrodebeing smaller than the opening in said insulator member 3 Vso that saidground electrode forms a restriction to the passage of electricaldischarges out of the spark gap.

2. An igniter comprisinga tubular metal shell, an insulator securedwithin said shell and havinga centerbore enlarged at one end thereof toform a recess, a metal centerwire within said centerbore terminatingwith a head portion positioned within said recess, an insulator memberhaving an opening therethrough and positioned in said re# cess, a centerelectrode positioned between said centerwire head portion and one sideof said insulator member, said center electrode having a projectionextending partially through the opening in said insulator member, and aground electrode having an opening therethrough aligned with the openingin said insulator member and positioned against the other side of saidinsulator member so as to be in spaced relationship to said projectionto form a spark gap therewith, at least one of said electrodes beingmade of carbon and the opening in said ground electrode being smallerthan the opening in said insulator member so that said ground electrodeforms a restriction to the passage of electrical discharges out of thespark gap.

3. An igniter comprising a tubular metal shell, an insulator securedwithin said shell and having a centerbore enlarged at one end thereof toform a recess, a metal centerwire within said centerbore terminatingwith a head portion positioned within said recess, an insulator ring insaid recess, a center electrode positioned between said centerwire headportion and one side of said insulator ring, said center electrodehaving a projection extending partially through the bore in saidinsulator ring, and an annular ground electrode positionedconcentrically against the other side of said insulator ring and inspaced relationship to said projection so as to form a spark gaptherewith, the internal diameter of said ground electrode being from 33%to 75% of the diameter of the bore in said insulator ring so that saidground electrode forms a restriction to the passage of electricaldischarges out of the spark gap. i

4. An igniter comprising a tubular metal shell, an elongated insulatorsecured within said shell, said insulator having a centerbore enlargedat one end thereof to form a recess, a metal centerwire within saidcenterbore terminating with a head portion positioned within saidrecess, an insulator ring in said recess, a carbon center electrodepositioned between and abutting said centerwire head por tion and oneside of said insulator ring, said center electrode having a projectionextending partially through the bore in said insulator ring, and acarbon ring-shaped ground electrode positioned concentrically againstthe other side of said insulator ring and in spaced relationship to saidprojection to frm a spark gap therewith, the itnernal diameter of saidground electrode being from 33% to 75% of the diameter of the bore insaid insulator ring so that said ground electrode forms a restriction tothe passage of electrical discharges out of the spark gap.

5. An igniter comprising a tubular metal shell internally threaded atone end thereof, an elongated insulator secured within said shell andhaving a centerbore enlarged at one end thereof to form a recess, ametal centerwire Y within said centerbore terminating with a headportion positioned within said recess, an insulator ring in said recess,a carbon center electrode positioned between and abutting saidcenterwire head portion and one side of said insulator ring, said centerelectrode having a projection extending partially through the bore insaid insulator ring, a carbon ring-shaped ground electrode positionedconcentrically against the other side of said insulator ring and inspaced relationship to said projection to form a spark gap therewith,and a retainer ring threadedly en gaged with the end of said shell andbearing against said ground electrode to maintain said center electrode,said insulator ring and said ground electrode in assembled relationship,the internal diameter of said ground electrode being from 33% to 75% ofthe diameter of the bore in said insulator ring so that said groundelectrode forms a restriction to the passage of electrical dischargesout of the spark gap.

6. An igniter comprising a tubular metal shell, an insulator securedwithin said shell and having a centerbore enlarged at one end thereof toform a recess, an insulator member having an opening therethrough andpositioned in said recess, a center electrode positioned in said recessabove said insulator member, said center electrode having a projectionextending partially through the opening in said insulator member, vand aground electrode having an opening therethrough aligned with the openingin said insulator member and positioned below said insulator member soas to be in spaced relationship to said projection to form a spark gaptherewith, the opening in said ground electrode being smaller than theopening in said insulator member so that said ground electrode forms arestriction to the passage of electrical discharges out of the sparkgap.

No references cited.

